Carriers of this type are known to a sufficient extent from the prior art. They may be formed either as a gripper hand on a tool changer or as a storage space in a tool magazine. They serve to move a tool holder, which as a rule is a standardized steep-taper tool holder or a hollow shank taper tool holder and on its lower shank bears a machining tool, rapidly towards a working spindle or away from it.
At their upper end, the standardized tool holders have a conical section with which they are inserted into a corresponding tool-holding fixture on the end side of a working spindle. The conical upper section is adjoined by a thickened, cylindrical collar which is provided with an encircling gripper groove at which the tool holders are grasped by the carriers. The shank in which the machining tool is held adjoins the bottom of the cylindrical collar.
As already mentioned, the carrier may be formed as a gripper hand on a tool changer, which removes tool holders from a tool magazine and inserts them into the tool-holding fixture on the working spindle, or removes tool holders from the tool-holding fixture and deposits them again into the tool magazine.
Machine tools are known, in which a tool changer is provided with a gripper hand, so that first of all a tool holder is removed together with a machining tool which was previously in use from the tool-holding fixture and is deposited into an empty space in the tool magazine before a new tool holder is removed from the tool magazine and is inserted into the tool-holding fixture. In the case of other known machine tools, two tool changers are provided which operate in a push-pull action, with the result that the one gripper hand is already moving a tool holder, which has been removed from the tool magazine, towards the working spindle while the other gripper hand is removing the tool holder which has previously been clamped in place on the tool-holding fixture, and is transporting it to the tool magazine.
In addition, machine tools are known, in which the changing of tools takes place by the pick-up method, in which the working spindle directly approaches a changing position on the tool magazine and there first of all deposits the clamped-in tool holder into an empty space, whereupon the tool magazine moves a new tool holder to the changing position where it is “picked up” by the working spindle.
Gripper hands described in this respect and the storage spaces in the tool magazine are formed in each case by the carriers which are mentioned at the beginning and in which the tool holders are retained in a form-fitting manner by means of the at least one movable jaw.
This form-fitting retention of the tool holders in the carriers is important not only for the operating reliability of the known machine tools, but also for the speed at which a changing of tools can take place. This is because the more rapidly the storage spaces in a tool magazine can be moved and/or the more rapidly a gripper hand can be moved between the tool magazine and the tool-holding fixture on the working spindle, the more rapidly can a machining tool which is in use be interchanged for a new machining tool.
Due to the high accelerations which occur during the moving of the tool magazine and/or the moving of the gripper hand, it is imperative for the tool holders to be securely grasped in the carriers. A tool holder which falls out of a carrier leads not only to a stoppage in the machining process, but may also cause considerable damage to the machine tool and, in the most unfavourable situation, may even cause injury to people.
However, the abovementioned damage is caused not only by the tool holders falling out; also, a tool holder which is only partially released from the carrier generally results in the machining operation having to be broken off because the tool holder is now no longer inserted in the correct position into the working spindle or placed into the magazine.
For this purpose, most known carriers have two movable jaws which are prestressed into their closed position by tension or compression springs. In this case, the spring force determines the force with which the tool holders are retained in the carrier, since the form-fitting connection is not self-locking and, upon corresponding accelerations, the tool holder presses the movable jaws in the direction of their expanded position, which is only prevented by the force of the tension or compression springs. If the springs break off or alter, this results in the tool holders no longer being securely retained in the known carriers.
DE 37 17 201 A1 discloses a carrier in the form of a gripper hand having two fixed jaws which grasp a tool holder at its gripper groove and retain it in the axial direction. Two movable jaws are arranged pivotably on the two fixed jaws and are opened and closed via a positively controlled mechanism about axes parallel to the longitudinal axis of the tool holder. The mechanism is driven via the axial movement of an actuating member and is prestressed into its closed position by means of a compression spring. In the expanded position of the movable jaws, the tool holder can be pulled laterally out of the fixed jaws transversely with respect to its longitudinal direction.
In the case of this carrier, it is also disadvantageous that, when the clamping force of the spring slackens, the closing force and therefore the retaining force diminish, or are completely lost if the spring breaks. As far as the closing of the movable jaws is concerned, the known carrier is dependent on the reliability of the compression spring.
In addition, the spring force is often also not sufficient in order to close the movable jaws. This occurs in particular if the mechanism is jammed by chips which have passed into the gripper hand. In these situations, when the gripper hand is moved, the tool may fall out of the gripper hand and cause the abovementioned damage to the machine tool.
A carrier disclosed in DE 40 36 915 A1 avoids these disadvantages in the case of a carrier as disclosed in DE 37 17 201 A1 by the fact that the mechanism is not actuated via a compression spring but rather via a coupling mechanism which temporarily connects the gripper hand to a spatially fixed stop. Movement of the coupled-up gripper hand in relation to the spatially fixed stop causes the mechanism to be actuated, as a result of which the movable jaws are pivoted between their expanded position and their closed position.
Although this carrier avoids the disadvantages which are associated with jaws prestressed via springs, it is nevertheless a very complicated design in terms of structure, the changing of tools taking place very slowly because of the coupling-up and the measures associated therewith.
However, DE 195 37 071 A1 also describes a carrier in the form of a gripper hand which is arranged on a tool changer and transfers tool holders between a tool-holding fixture on a working spindle, and a tool magazine. This carrier has two movable jaws which can be pivoted about a pivot axis, running parallel to the longitudinal axis of the tool holders, between an expanded position and a closed position. Instead of the above-described two fixed jaws, a clamping block is provided which, after a complicated tool-changing process, fixes the tool holder in the axial direction if it is already inserted by its taper into a tool-holding fixture. The two movable jaws are pivoted via a pneumatic, hydraulic or electromechanical drive.
In the case of this carrier, it is disadvantageous that, firstly, it is very complicated in terms of structure and, secondly, has a high weight, so that it makes only a slow changing of tools possible because of the heavy mass which is to be moved. Furthermore, due to the interaction of clamping block and tool-holding fixture, the moving is relatively complicated plicated and has to be checked via sensors, so that the changing of tools can also take place slowly because of this.
DE 199 19 446 A1 describes a carrier which is designed as a magazine space in a tool magazine. In the case of this known carrier, the tool holder is introduced transversely between two fixed jaws and is then lowered into a depression provided on the jaws where it is retained by means of its dead weight. The changing of tools takes place here by the pick-up method, the working spindle entering a tool holder which is to be interchanged laterally and transversely into the carrier which, in the process, engages with its fixed jaws into the gripper groove of the tool holder on opposite sides. When the tool holder is completely pushed in transversely, it is lowered, so that it comes to lie in the depression.
Although this construction is very simple, it does not permit rapid movement of the carrier, since the tool holder is only retained by means of its dead weight.
Document EP 1 179 387 A discloses a carrier having two fixed jaws defining an opening into which a tool holder is inserted laterally. Further provided is a C-shaped claw that is pivoted from above around a pivot axis running transversely with respect to a direction along which said tool holder is inserted into said carrier. Said tool holder has a diameter becoming larger in the direction of the carrier, so that said claw grasps around said larger diameter of said tool holder. For opening said carrier, said claw is pivoted to the above in active manner using a working piston. Said pivoting down onto said carrier is supported by a tension spring.
Further to the complicated design it is a disadvantage of the known carrier that said claw can be pressed against the tension force in its open position since the tool holder is tapering in a direction away from the carrier.